As Eric mentioned in a comment, the issue is degree of disclosure. It can be a subtle issue. A publication that explained a result but did not show how to achieve the result would not be novelty breaking.
If you think that might be your situation you can file an application and provide the USPTO with all of the information about the publication. Dates, content and the details of "publication".
There are strange edge cases in the US. A thesis that has been shelved in a university library by subject has been published but if the only public copy is shelved by student's name it is not published. A printed journal is published the day is is received in the mail by someone.
Another situation (not yours involves pubic demonstrations. In the case of a public demonstration (public = at least one person not under an agreement of confidentiality) the workings of a device need not be exposed in order for novelty to be broken - in the U.S.
That is becasue the section 102 wording is
- the claimed invention was patented, described in a printed
publication, or in public use, on sale, or otherwise available to the
public before the effective filing date of the claimed invention;
A US patent can be barred (after 1 year) by offer for sale, public use, and sales that do not disclose anything about the invention. Demonstrations are public use unless the experimental exception can be shown.
Outside the U.S. a demonstration that divulged no inner workings would not break novelty.
A slide show at a conference with no handouts is probably not published. A poster on a wall at a conference that is up for a day (no handouts) might or might not be published. In some of the world demonstrations at a handful of specific trade shows is not initially novelty breaking.
And, very important for the US, there is a, sort of, one year grace period after publication.